Conventionally, a device having a variety of structures to detect an amount of an intake air (i.e., a flow rate of an intake air) supplied to an engine is coupled to an intake device for the engine mounted to a vehicle such as an automotive.
A flow rate measuring device is a representative device that is a so-called air flow meter. The flow rate measuring device is disposed in an intake passage between an air cleaner, which draws a fresh air as an intake air, and a throttle body, which controls the flow rate of the intake air. The flow rate measuring device measures a flow rate of the intake air.
The device generally includes a bypass passage, a flow rate sensor, and a measurement body. The bypass passage draws, as a measurement flow, a portion of a main flow (an intake air flow) flowing through an intake passage (hereinafter, may be referred to as a duct as well). The flow rate sensor is disposed in the bypass passage and measures a flow rate of the measurement flow. The measurement body is disposed inside the duct and defines the bypass passage.
The measurement body includes a measurement inlet, a measurement outlet, and a cylindrical portion. The measurement inlet is open toward the upstream side of the duct and guides the measurement flow into the bypass passage. The measurement outlet is open toward the downstream side of the duct and discharges the measurement flow. The cylindrical portion is disposed to cover the measurement outlet and guides the measurement flow.
In the automotive technology field, a demand for improving performance of mounted devices is very high as technology in this field develops. Above all, high accuracy for measurement performance (flow rate measuring function) is strictly requested in the flow rate measuring devices.
In view of this, a variety of modifications or improvements have been conducted to increase the accuracy of measuring a flow rate. For example, (i) changing the shape of the bypass passage to suppress pulsation of the measurement flow or changing the length of the bypass passage, (ii) improving surrounding components around the flow rate measuring device to prevent a counter flow element from entering into the bypass passage, or (iii) devising the structure of a flow rate sensor to increase the accuracy of detection, have been conducted.
However, higher accuracy of measuring function is strongly required toward the flow rate measuring devices as engine performance further increases recently.
In view of the above, it is an objective of the present disclosure to provide a flow rate measuring device that is capable of measuring a flow rate with high accuracy.